The ability of Schwann cells to express myelin specific proteins and synthesize myelin lipids is dependent on continued axonal contact. The axonal molecules which are responsible for this effect are completely unknown. Using axolemma-enriched fractions (AEF) and cultured Schwann cells, the specific axonal molecules responsible for the increased expression of the myelin specific PO mRNA and for the increased synthesis of the myelin galactocerebroside in Schwann cells will be identified. Detergent will be used to solubilize AEF so as to preserve the functional activity. Using the polymerase chain methodology, a specific and sensitive assay will be developed to measure the axolemma-enriched fraction induced increase in PO mRNA. An assay will be developed to measure axolemma-enriched fraction stimulation of incorporation of lipid precursors into galactocerebroside. Using these assays to follow the activity, the solubilized preparations will be fractionated by column chromatography in order to isolate the specific axolemmal molecule(s) which mediate these two Schwann cell responses. The mechanism by which axolemma-enriched fraction increases the level of PO mRNA will be determined (transcriptional Activation or increased stability of mRNA or a combination of both mechanisms) . The developmental expression of these molecules in axolemma will be studied as well as the developmental response of Schwann cells to the axolemmal molecule. Monoclonal and polyclonal antibodies will be raised to the axolemma-enriched fractions. The ability of these antibodies to block the interaction of Schwann cells and axons in culture will be evaluated. These studies will determine the identity and developmental regulation for these important functional molecules associated with the axon. The response of the immune system to the axonal plasma membrane as an antigen will be established. This information is important since the axon is a likely target in immune mediated disease and the molecules which mediate axon-Schwann cell interactions may be compromised in a number of peripheral nerve diseases.